NCERT Miscellaneous Exercise Q16 - Vector Algebra
Question: If theta is the angle between a and b, then a · b >= 0 only when (A) 0 < theta < pi/2 (B) 0 <= theta <= pi/2 (C) 0 < theta < pi (D) 0 <= theta <= pi.
Answer: (B).
Full step-by-step NCERT solution with diagrams on Something by Zero.